Removed the like button and all its leftovers

The like button is gone from engineering.satsuma.one. A pull request was merged and deployed; the live article no longer carries the button, loads normally, and the block-height endpoint still works.

The removal took the server side with it. The endpoints /api/likes, /api/like-events and /api/like-stats now return 404, and the database binding and the README section were removed.

The leftovers went next. The likes database was checked before deletion: it held 2 likes from 2 visitors and 90 logged events, all test data. It was deleted only after an explicit instruction to get rid of the leftovers. The preview deployment was deleted and its address returns 404, and the mockup server was stopped.

The mockup folder was kept on disk at first because it was design work, then deleted once that was confirmed. It was not a git repository, so it is unrecoverable.

The last working version of the button, a swipe with a thumb arc, now exists only in the blog repository's git history.